Vehicle radar system

ABSTRACT

A radar system adapted to be installed on a vehicle ( 1 ) is operable to detect objects in different fields of view of the system. The system has transceiver means ( 2, 3; 44, 46 ) for transmitting a radar signal and receiving the signal after the latter has been reflected from an object to be detected. A reflected signal is sampled by sampling means ( 12; 66 ) during a succession of sampling periods each of which is delayed with respect to a corresponding portion of the transmitted signal. The gating of the reflected signal effectively generates range shells, each of which corresponds to the time taken for a transmitted signal to reach an object at the shell, and to be reflected back to the system and is hence related to the delay between the transmission of the signal and the corresponding sampling period. The range shells define the field of view of the system, which can be changed by altering said delay. Such alterations are carried out under the control of control means which is connected to sensor means for detecting a property of the operation of the vehicle, determining a required position of the field of view, and setting the field of view of the system accordingly. The range shell positions, and hence fields of view, can also be changed by selecting alternative transmitters and/or receivers of the transceiver means. There is also shown a motor road vehicle which has a radar system comprising a pair of transmitter antennas at two alternate corner regions of the vehicle and a pair of cooperating receiver antennas of the other two corner regions. Certain embodiments of the system also have the facility to generate range shells which are swept over an area around the vehicle or which track detected objects.

FIELD OF THE INVENTION

This invention relates to a radar system adapted to be installed on amachine or vehicle, particularly a motor road vehicle, and to such avehicle fitted with a radar system.

BACKGROUND TO THE INVENTION

It has been proposed to install radar systems in motor road vehicles andon other machinery for detecting objects of various kinds. Such systemsgenerally use co-located and closely coupled transmitters and receiverswhich are arranged to detect the presence or approach of objects in aparticular direction or situation, for example, when a vehicle isreversing.

However, known systems have tended to be expensive and tend only to beuseful in a narrowly specified set of situations.

THE INVENTION

According to the first aspect of the invention, there is provided aradar system adapted to be installed on a vehicle (preferably a motorroad vehicle) and operable to detect objects in differing fields of viewof the system, the system comprising transmitter means for transmittinga radar signal; receiver means for receiving the signal after the latterhas been reflected from the reflecting surface of an object to bedetected; gating means for sampling the reflected signal received by thereceiving means during a succession of sampling periods, each of whichis delayed with respect to a respective portion of the transmittedsignal by a time delay corresponding to the time taken for that portionto travel to the reflecting surface when the latter is at a notionalrange shell, and then back to the receiving means, so that a reflectedsignal received during that period is indicative of the presence of areflecting surface at the range shell; control means for controlling thefield of view of the system and sensor means which is connected to thecontrol means and is operable to detect one or more features of theoperation of the vehicle, which features are characteristic of therequired field of view of the system wherein the control means in usedetermines said required field of view and sets the field of view of thesystem accordingly, in dependence on the output of the sensor means.

A single antenna may comprise both the transmitter means and thereceiver means, but preferably the transmitter means and receiver meanscomprise a plurality of antennas.

The field of view of the system corresponds to the position(s) of therange shell relative to the vehicle, and hence defines the possiblepositions of any object which can be detected by the system.

Thus, if the system has only one transmitter and one receiver arrangedonly to detect objects in one sector relative to the vehicle (forexample behind the vehicle), the alteration of the field of view isachieved simply by altering the distance of the range shell from thevehicle. If, however, the system has a plurality of suitably positionedtransmitters or receivers, the angular position of a current range shellrelative to the vehicle will depend on which transmitter and receiverare being used, and can be correspondingly altered by using anotherreceiver or transmitter, thus also altering the field of view of thesystem.

Accordingly, depending on the configuration of the transmitter andreceiver means, said control of the field of view of the system isachieved by controlling either the distance (i.e. range) of each rangeshell or by selection of the antenna (or pairs of antennas) andassociated antenna beams to be used, thereby controlling angularposition of the range shell or by controlling both distance and angularposition of the range shell.

Preferably, the radar system comprises a pulsed radar system, in whichthe transmitted signal comprises a succession of pulses, each of whichconstitutes a respective one of said portions of the transmitted signal.

Preferably, the control means is operable to detect fluctuations in thesignal received in a succession of sampling periods, said fluctuationscorresponding to an object entering or leaving a range shell.Alternatively, the control means may be operable to detect any DC offsetof signal received over a succession of sampling periods with respect toa reference level to determine whether there is an object at the rangeshell which object is stationary relative to the range shell.

In the former case, the control means is preferably operable also toanalyse the received signals to determine the principal frequencythereof, or the time delay between detections at different range shells,and hence to estimate the velocity of the object relative to the rangeshells.

Preferably, the transmitter and receiver means are adapted to be mountedon the vehicle in positions which are such that, in use, the system candetect a presence of objects at any position around the vehicle.

To that end, the transmitter means and receiver means are preferablymountable in the regions of the corners of the vehicle, and areconveniently adapted to be incorporated into the vehicle bumpers.

In such a case the system can detect objects in front of, to the sidesof and behind the vehicle.

This can be achieved by transmitter means comprising two antennasadapted to be mounted at diagonally opposite corner regions of thevehicle, and receiver means comprising two antennas adapted to bemounted at the other corner regions of the vehicle.

Thus, the rear transmitter antenna is used to provide signals which arereflected from objects behind the vehicle and received by the receiverantenna at the other rear corner, and also provides signals which areused to detect objects to its own side of the vehicle and are receivedat the receiver antenna on the front corner on the same side. Similarly,the forward transmitter antenna can provide the signals which are usedto detect objects in front of and to the other side of the vehicle. Thisfeature therefore enables a relatively large area of coverage to beachieved using fewer transmitter/receiver antennas than would be thecase if the system used co-located transmitter and receiver antennas.

The sensor means may include sensors responsive to the operation of thedirection indicators or to steering wheel movement of the vehicle, or tothe operation of the vehicle brakes.

In the latter case, the control means may be so arranged that, when thevehicle brakes are operating, the range shells are positioned relativelyclose to the vehicle. The sensors responsive to the operation of thedirection indicators or to steering wheel movement can cause a selectionof range shells to the side of the vehicle on which the indicators areoperating or towards which the wheel is turned, as the case may be.

The sensor means may additional or alternatively determine the speed ofthe vehicle, the distance of the range gates from the vehicle increasingif the detected speed of the vehicle increases.

The sensor means may include a sensor for determining whether reversegear has been selected on the vehicle, in response to which the controlmeans is operable to activate the rear antennas of the vehicle.

Additionally or alternatively, the sensor means may to advantage beoperable to determine the speed with which the vehicle is reversing.

In such a case, the control means is preferably operable to set therange shell, when the vehicle is reversing, at a distance whichincreases with increasing speed, in accordance with a predeterminedrelationship.

Preferably, that relationship is such that the range shell distance isdirectly proportional to the speed of reversing, subject to a minimumrange shell distance when the vehicle is stationary or slow moving.

Additionally or alternatively, the control means progressively increasesor decreases said time delay for successive periods so that thedistances of successive range shells increases or decreases between saidpredetermined minimum distance and the maximum distance determined inaccordance with said relationship, so that the range shells sweep thearea between said minimum and maximum scan distances. Such a successionof range shells will be referred to as a scanning range shell.

The rate at which said time delay is increased or decreased may be inproportion to the vehicle speed and/or related to vehicle direction.Furthermore, if the vehicle is moving forwards, the delays in thesampling of the output of the forward antenna may progressivelydecrease, thus causing the scanning shell in front of the vehicle tomove inwards towards the vehicle, whilst the delays associated with therear receiver antenna progressively increase so that the rear shellscans away from the rear of the vehicle. The front and rear shells mayscan in opposite directions if the vehicle is reversing.

In either case, the scanning direction of any of the scanning shellspreferably is such as to reduce the speed of motion of the shell so ascorrespondingly to reduce the doppler shifted frequency(ies) of anysignal reflected from the shell. This in turn reduces the noisebandwidth of the system.

Such scanning also enables the system to detect objects which, when atthe maximum distance are to one side of the area to which the system issensitive, but which subsequently move, relative to the vehicle,sideways into the path of the vehicle, (for example when the vehicle isreversing around a corner).

According to a second aspect of the invention, there is provided avehicle fitted with a pulsed radar detection system comprising twotransmission antennas operable to transmit a series of pulses, andmounted at diagonally opposed corner regions of the vehicle, and tworeception antennas, which are operable to receive pulses reflected fromother objects and which are mounted at the other corner regions of thevehicle.

Preferably, on detection of an object at a given shell, the controlmeans is operable to control said time delays so that the correspondingrange shells all extend into the vicinity of the object so that therange shells, in effect, track the object.

In this case, the reduction of range shells is then in part governed bythe detection of objects at previous shells.

The invention also lies in a vehicle fitted with a radar system withboth transmitters and receivers at all (four or more) corners of thevehicle.

The invention also provides a radar system adapted to be installed on avehicle and operable to detect objects in differing fields of view ofthe system, the system comprising transmitter and antenna means fortransmitting radar signals, receiver and antenna means for receivingsuch signals; means for detecting the presence or absence of areflecting target at a pre-determined set of ellipsoidal range shellsaround the vehicle; selector means for selecting the field of view ofthe system and sensor means connected to the selector means and operableto detect one or more features of the state of operation of the vehicle,which features determine the required field of view.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a plan diagrammatic view of a motor car fitted with a radarsystem in accordance with the invention, the system being arranged todetect objects to the rear of the car;

FIG. 2 is a block diagram of the radar system shown in FIG. 1;

FIG. 3 is a block diagram of a modified version of the system;

FIG. 4 is a diagrammatic side view of the vehicle shown in FIG. 1,illustrating the operation of the modified version of the radar system,and in particular the range gates generated thereby;

FIG. 5 is a graph showing the relation ship between the distance of oneof the range gates shown in FIG. 4 to the speed at which the car isreversing;

FIG. 6 is a diagrammatic plan view of a car fitted with a furthermodified version of the system, and illustrates some of the range shellswhich can be generated by the system, the system being capable ofdetecting objects in front of, behind or to the sides of the vehicle.

FIG. 7 shows a further modification to a system in accordance with theinvention, the modification enabling the system to locate obstaclesbehind the vehicle; and

FIGS. 8 and 9 show the “stereo signature” produced by the system ondetection of a car.

DETAILED DESCRIPTION

With reference to FIG. 1, a motor car 1 is fitted with a radar systemcomprising a transmit antenna 2 and a receive antenna 3. Both antennasare of the flat conformal type, and are mounted in the rear bumper 5 ofthe car. The transmit and receive antennas are respectively positionedat the regions of the rear nearside and rear offside corners of the car.

In use, the antenna 2 transmits a series of short radio frequencypulses, each of which is typically of 0.1 to 5 nanoseconds' durationdepending upon the rise and fall times and the frequency responsecharacteristics of the antenna 2. In general, each pulse consists ofonly a few cycles of the dominant radio frequency. However, the pulsesare to be distinguished from those used by the class of “ultra-widebandradars”, in which a transient waveform contains a very wide spectrum offrequencies, and is unlikely to meet electromagnetic compatibilityrequirements. The frequency of occurrence of the pulses is of the orderof MHz.

With reference to FIG. 2, the transmission of pulses by the antenna 2 isinitiated by a timing generator 4 which, by means of a stableoscillator, triggers a transmitter generator 8 of a transmitter 8 to theantenna 2 via band pass frequency filtering means 10.

Before being transmitted by the antenna 2, the pulses generated by thegenerator filtered in the filtering means 10 to which allows frequenciesin an operating band of 5.7-7.2 GHz to pass to the antenna fortransmission.

The timing generator 4 is also connected to a gating receiver 12 whichis, in turn, connected to the receive antenna 3 via amplifying andfiltering means 14, which amplifies and filters the signals received bythe antenna 3, to pass the same band of frequencies as are passed by thefilter 10.

The gating receiver 12, in response to a signal from the timinggenerator 4, samples the signals received by the antenna 3 after thosesignals have been filtered and amplified.

The output from the gating receiver 12 is connected to a detectorcircuit 28 which determines the presence or absence of an obstacledepending upon whether a reflected signal has been received by theantenna 3, and generates an output 0 representative of the presence orabsence of such a reflection. The operation of the detector 28, timinggenerator 4 (and hence the transmitter 8 and the receiver 12) iscontrolled by means of a selector 32 which receives signals from asensor 30 which provides signals indicating the state ofcontrol/operation of the vehicle. In the illustrated embodiment, thesensor 30 is a speed sensor which detects the speed at which the vehicle1 is reversing. The selector 32 controls the delay between thegeneration of each transmitted pulse and the respective gating of theoutput from the amplifier/filter 14 in accordance with the relationshipdiscussed below.

In general, the timing generator 4, acting under the control of theselector 32, causes the gating receiver 12 to sample the output of thereceive antenna 3 for a predetermined period (a sampling period of, forexample, 0.05-2.5 nanoseconds) at one or more predetermined delays(normally of 1 to 200 nanoseconds corresponding to ranges of 15 cm to 30m behind the vehicle) after the transmission of a given pulse by theantenna 2. If the antenna 3 receives the reflection of such a pulseduring a given sampling period, this is indicative of the transmit pulsehaving travelled from the antenna 2 to a reflecting surface and back tothe antenna 3 in the delay between the transmission of the pulse and therespective sampling period.

From this information, it can be deduced that the reflecting surfacelies somewhere on a range shell (hereinafter referred to as a rangegate), for example the range gate 33 in FIG. 1, the distance of whichfrom the car 1 is such that the time taken for a pulse to travel to therange gate and back to the car 1 is the same as the delay between thetransmission of the pulse and that sampling period.

Thus, the range gate can be considered to be in the form of a partellipsoidal shell having antennas 2 and 3 at its focii. The range gatedoes not take the form of a full ellipse enveloping the car 1 becausethe transmit and receive antennas 2 and 3 do not provide all roundcoverage. In fact, the lateral extent of the range of the system isdetermined by multiplying together the beam patterns of the antennas. InFIG. 1, the shaded area 6 is the portion of the area in the range of thesystem between the gate 33 and the car 1.

The distance of the range gate 33 from the rear of the car 1 isdetermined by the selector 32 in accordance with the relationshipillustrated in FIG. 5. Thus, when the vehicle reversing speed is lessthan I meter per second, the range gate 33 is set at a predeterminedminimum distance of 2 meters from the rear of the car 1 as indicated bythe horizontal portion 31 of the graph. However, as reversing speedincreases, so the driver of the car needs to be warned of obstaclesfurther away from the rear in order to have time to stop the car ifnecessary. Therefore, as the reversing speed increases beyond 1 meterper second, the distance of the range gate 33 correspondingly increases,as indicated by the sloped portion 35 of the graph.

The system shown in FIG. 3 is similar in many respects to the system inFIG. 2. However, the system has a number of gating devices, for example62, 64 and 70 connected to a receive antenna 53 (corresponding to theantenna 3) for receiving reflections of pulses transmitted by atransmitter antenna 52 (corresponding to the antenna 2).

The transmission of pulses by the antenna 52 is initiated by timinggenerator 54 which, by means of a stable oscillator, triggers a transmitgenerator 56 of a transmitter 58 connected to the antenna 52. Thosepulses are similar to the pulses generated by the transmitter 8 and,before being fed to the antenna 52, are filtered in a band-pass filter60 to remove frequency components which would interfere with nearbyradio equipment in the same or other vehicles.

The timing generator 54 is also connected to the gating devices 62, 64and 70, each of which includes a respective sampler 66 which samples theoutput of the antenna 53 in response to a signal from the timinggenerator 54. RF filters 68 connected between the samplers 66 and theantenna 53 filter any signals received by the latter to removeinterference from continuous wave sources, for example radio broadcastsor mobile phone transmissions. The gating devices 62, 64 and 70 allinclude amplification means (not shown) for amplifying the receivedsignals.

The outputs of the gating devices 62, 64 and 70 are connected torespective signal processing units 72, 74 and 76 which then feed theprocessed signals to control means in the form of a control processor 78for analysing signals from the processors to determine whether or not toinitiate the operation of a Man Machine Interface 80 which may be avisual or audible alarm.

Each signal processing unit thus incorporates a respective receiver fordetecting signals received through the gating devices, the bandwidth ofthe receiver being variable depending upon the nature of the signal tobe analysed. The control processor 78 also sends signals to the timinggenerator 54 for causing the latter to initiate the transmission ofpulses and the sampling of the output from the antenna by the gatingdevices 62, 64 and 70 at times controlled by the processor 78.

The processor 78 is also connected to a motion sensor (not shown) whichmeasures the speed with which the car 1 is reversing.

In use, the timing generator 54 causes a selected one of the gatingdevices to sample the output of the receive antenna 53 during arelatively short sampling period, preferably less than the rise time ofthe edge used to generate the transmit pulse at a predetermined delay(normally of 1 to 200 nanoseconds corresponding to ranges of 15 cm to 30m), thus creating an associated range shell in a similar fashion to thesystem of FIGS. 1 and 2.

The control means is adaptable to provide time delays which may be fixedfor a given vehicle speed, which may increase or decrease regularly withtime (to produce a scanning range gate), which may vary so that therange gate moves to track an obstacle which has been detected by thesystem, or which may vary in response to the movement of the vehicleitself. The control means may further contain circuits which, while thetime delay for the range gate increases or decreases regularly betweenminimum and maximum values, further sampling is carried out to allow theanalysis of signals corresponding to particular fixed or adjustablevalues of delay.

With reference to FIG. 4, each gating device produces a respective rangegate. The gating device 64 produces the gate 33 which is at a fixeddistance (for at least 1000 operating cycles of the system) from therear of the car 1, for a given reversing speed. The relationship betweenthe distance of the gate 33 from the rear of the car is the same as thatfor the gate 33 produced by the system of FIGS. 1 and 2.

The gating device 62 is controlled to sample the output from the antenna53 at successive sampling periods which occur at successively increasingdelays from their respective pulses. For example, if the first samplingperiod of the device 62 occurs 10 nanoseconds after the transmission ofthe corresponding pulse, the time delay between the transmission of thenext pulse and the next sampling period might be 11 nanoseconds, andthis increase in delay can continue until a maximum is reached,whereupon the minimum delay is used once more.

As a result, the gating device 62 produces a range gate which scans anarea behind a vehicle. Two possible positions of the scanning range gateare indicated at 34 and 36 in FIG. 4. In this example, the scanningrange gate scans from 0.1 meters behind the vehicle to the position ofthe ‘fixed’ range gate. Thus, for example, for reversing speeds up to 1meter per second, the scan range will be 0.1 to 2 meters. The scanninggate sweeps along the shaded zone 6 shown in FIG. 1.

The scanning range gate enables the radar system to detect a movingobstacle such as the obstacle 40 in FIG. 1 which lies outside thelateral range of the gate 33 when at that distance, but which moves intothe path of the car after the range gate 33 has passed by. Such anobject will not be detected at the range gate 32 produced by the gatingdevice 64, but will be detected at the scanning range gate produced bythe gating device 62.

One of the other gating devices can be used to produce a range gatewhich tracks an object which has been detected behind the car, thusproviding an accurate indication of the rate of approach of that objectrelative to the car. This is achieved by continuously adjusting thesampling delay for the gating device in question under the control ofthe processor 78. In one example, the tracking range gate (such as thegate 42 in FIG. 4) takes the form of a scanning range gate which sweepsbetween relatively small limits which are adjusted after each scan basedon the output of the sampler.

A possible algorithm for use in determining the limits is one whichmeasures the position of the highest peak in the received signatureafter each scan and the width of the peak (between adjacent minima orzero crossings, for example). The peak position and its change over anumber of scans can be used to obtain an estimate of the target positionand velocity, using algorithms such as Kalman filtering. A predictioncan then be made of the object position for the next scan and the scanlimits set on either side of that predicted position. The scan limitsare also set to take into account the possibility of prediction errorsand the width of the peak to ensure that the same peak is found in thenext scan.

Forward movement of the car is detected by the sensor connected to thecontrol processor 78. In that event, the processor 78 sets a fixed reargate 33 at a distance which is greater than the distance as indicated bythe graph in FIG. 5, and which is independent of vehicle speed. Therange gate is then used to detect vehicles approaching the car from therear, so that the system can, if necessary, warn the driver of the car lnot to change lanes or overtake other vehicles.

The processor 78 can analyse the received reflected signals to obtain anindication of the velocity of the other vehicle relative to the rangegate 33 using the relationship

υ=2v/λHz

Where υ is the dominant frequency of the received signal, v is thevelocity of the other vehicle normal to the range gate and λ is thedominant wave length of the radiated pulses.

In addition, the system can detect the presence of a static object at afixed position, relative to the car 1, using a corresponding fixed rangegate. To do this, the system measures the change in the level of thereceived signal and the receiver compared to the background levelmeasured in the absence of an object. This requires good long termstability of the receiver circuitry and that the receiver output beDC-coupled. Such an object can also be detected using a scanning rangegate since this will provide a corresponding signal to that produced bya moving object passing through a fixed range gate.

If the radar is using pulses of 1 nanosecond duration, and an object ismoving relative to a range gate with a speed of 10 meters per second,the dominant energy in the sampled signal will be at a frequency ofapproximately 67 Hz. In practice, the receiver band width for the systemmight be set from DC to 200 Hz or more in order that objects moving at arange of speeds of interest might be detected.

In general, scanning or tracking range gates (as described above) aremore appropriate for detecting objects fixed relative to the car 1 thanare fixed range gates because the objects do not then give rise to a DCsignal, and as a result the receiving circuitry of the system needsneither to be DC-coupled nor to have good long term stability.Furthermore, the receiver circuitry does not need to have as large abandwidth as the circuitry required to detect DC offset, particularly iftracking range gates are used (since their sweep velocity is relativelylow). The reduced bandwidth can be used to reject noise both in thereceiving circuitry and from external sources, thus improving the signalto noise ratio (particularly if tracking range gates are used, as theselower the doppler bandwidth of the received signal) of the system,compared with fixed range gates.

It will be appreciated that the nature of the range gate generated byeach gating device is governed by the control processor 78. Thus, eachgating device can produce fixed, scanning or tracking range gates,depending on the signal fed thereto by the control processor 78.

A further discussion of the possible uses of range gates and subsequentanalysis is set out below:

The presence of an object at a fixed position (relative to the car 1)can also be detected by using a range gate sweeping between delayseither side of that corresponding to the fixed position of interest. Thereceived signal is determined by the normal velocity of the objectrelative to the range gate, so that the centre-frequency of the receivercan be chosen using the above analysis where v is now the sweep-speed ofthe range gate. The receiver circuitry bandwidth will usually be chosento be comparable to the centre frequency, corresponding to the wide-bandnature of the transmitted radar pulse.

Using this method, stationary objects do not give rise to a DC signal,so that the receiver needs neither to be DC coupled nor to have goodlong-term stability.

Note that there are advantages in constraining the bandwidth of thereceiver circuitry as much as possible consistent with the receivedsignal in order to achieve rejection of noise, both due to thermal noisein the receiver circuitry and from external sources.

The presence of moving object can also be detected with a swept rangegate: the receiver bandwidth m ay need to be increased to allow forhigher (or lower) relative normal velocities of objects.

The range of an object can be measured by detecting its position at oneof a plurality of range gates (fixed or swept) formed by sampling atdifferent delays after the instant of transmission.

Static range gates could be formed at short spacings, preferably lessthan one-quarter of the wave length of the transmitted pulse. Forexample, to cover a region of interest extending to an upper range ofapproximately 10 m with a transmitted wavelength of 0.3 m might beachieved using 134 separate fixed range gates 0 m, 0.075 m, 0.15 m etc.

Swept range gates could also be formed at short spacings, either withoverlapping or non-overlapping sweeps, preferably not less than thewavelength of the transmitted pulse. For example, to cover a region ofinterest extending to an upper range of approximately 10 m with atransmitted wavelength of 0.3 m might be achieved using 33 separateswept range gates spanning the ranges 0-0.3 m, 0.3-0.6 m, 0.6-0.9 m,etc, or using the same number of separate swept range gates spanning therange 0-0.6 m, 0.3-0.9 m, 0.6-1.2 m, etc.

Using this method the range of an object can be determined from therange corresponding to the range gate on which it is detected. Inpractice, the extended signature of the object means that it is likelyto be detected at several range gates, in which case the median range ofthose gates can be used.

The range of an object can be determined with higher resolution by usinga smaller number of range gates which individually span a greater regionof interest, preferably more than four times the wavelength of thetransmitted pulse. As the range gate sweeps, the highest peak in thereceived signal (or some other identifiable feature) can be located. Therange of the object is determined from the sampler delay for the sampleat which the peak occurs.

More sophisticated signal processing techniques can be used to furtherincrease the range resolution.

For the range measurement of known objects, improved accuracy can beobtained by comparing the received signal with calibrated measuredsignatures, relating the position of the physical object to specificcharacteristics of its radar signature.

The motion of an object can be determined by measuring its change inposition or range over time, using techniques described above.

Signal processing techniques can be used to improve the resolution oraccuracy with which the motion of an object is determined, compared withdifferential position measurement which is inherently noisy.

The fixed and swept range gates discussed above have been generatedusing “open-loop” setting of the sampler delay and hence range gaterange: on the other hand, the sampler delay for the tracking range gatesis dependent on the reflected signals received, and is thus adapted tothe motion of the objects detected.

For example, the motion of an object can be determined by tracking it inrange with a swept range gate: the gate is repeatedly swept throughranges within which the object lies. At each sweep, the position andvelocity of the object is updated and the sweep range adjusted.

In a preferred embodiment, several configurable range gates will beprovided. One or more static range gates will be used in a“surveillance” mode for initial detection, following which a range gateand its associated sample can be assigned to tracking the motion of eachobject within the region of interest.

The system shown in FIG. 6 includes the features of the system of FIGS.1 and 2 (indicated by like reference numerals), and a furthertransmitter 44 and receiver 46 mounted in opposite end regions of thefront bumper of the car. A car fitted with the modified system thus hasan antenna in each of its four corner regions, each antenna having a 270degree field of view in the horizontal plane. A car fitted with thissystem thus has a respective antenna in each of its four corner regions.The shaded regions 6, 7, 9 and 11 represent the combined beam patternsof the antenna pairs 2 and 3, 44 and 46, 46 and 2 and 44 and 3respectively, when limited by the range shells 33, 56, 62 and 64respectively.

The antennas 44 and 46 are respectively connected to a number ofgating/amplifying devices and a pulse transmitter and filter, the kindshown (8, 10) in FIG. 2, and those components are in turn connected to atiming generator similar to the generator 4. The control processor forthe system (i.e. the selector 32) controls the operation of both pulsegenerators and all the gating devices, and selects which antennas andwhich gating devices are to be used depending on the condition of motionand control of the vehicle.

The antennas 44 and 46 thus can be used to generate range gates, such asthe gate 56 in front of the car. In addition, the antenna 3 can receivereflected signals transmitted by the antenna 44, whilst the antenna 46can receive reflected signals which were transmitted by the receiver 2so as to provide range gates to either side of the car 1. Thus, withjust two transmitters and two receivers, the radar system can detectobjects all around a car by virtue of being able to generate range gatesat the front, rear and sides of the car. When the car 1 is travellingforwards, the antennas 2 and 3 generate the rear fixed range gate 33 at,for example, thirty meters. The range gate 56 is one of a pair of rangegates 56 and 58, which scan the regions respectively in front of andbehind the car 1. Similar range gates (not shown) scan the regions toeither side of the car 1. If any of the scanning or fixed range gatesdetects another vehicle on the road, a tracking range gate, for example,62 or 64, so that the relative speed and position of the other vehiclecan be accurately monitored.

Thus, for example, if another vehicle being monitored by a forward rangegate suddenly decelerates, the associated increase in relative speed andreduction in distance from the car 1 can trigger an alarm. The selectorof the radar system is linked to the steering wheel sensors as a resultof which the system can determine if the driver of the car 1 is about tochange lanes and can warn the driver if this will result in a collisionrisk. Thus if, for example, the driver wishes to overtake the vehicleahead, the system will warn of the presence of the vehicle to the rightof the car 1.

The signals received from the same object at each two horizontallyspaced antennas (eg 3 and 46) as a result of reflection of the signalfrom the same transmitter antenna (eg antenna 2) are shown in FIGS. 8and 9. In this example, the object is equidistant from the receiveantennas leading to simultaneous detection of reflected pulses. In thecase of an off-centre object one of the graphs of FIGS. 8 and 9 will bedisplaced relative to the other along the time axis.

FIG. 7 shows a further modification to the radar system, in which eachcorner region of the car includes four antennas, one transmitter antennaand three associated receiver antennas. The Figure shows the front ofthe car and, in detail, the group of antennas on the front right cornerregion. As can be seen, that group has one transmitter antenna 100positioned just beneath two laterally spaced receive antennas 102 and104, and above a third receive antenna 106 which is vertically andlaterally spaced from the antennas 102 and 104. The transmit antenna isconnected to a transmitter and filter similar to the transmitter 8 andfilter 10, whilst each of the receive antennas, 102, 104 and 106 isconnected to a respective gating receiver and amplifier/filter similarto the receiver 12 and amplifier/filter 14, such that each of thereceive antennas can be used to generate a respective range gate inconjunction with the transmit antenna 100. The spacial separation of theantennas provides three ranges to the principal reflecting point on anobstacle, for example 108 in front of the car 1, and the system cantherefore be used to determine the position of the object by means oftriangulation.

The lengths of and angles between notional lines joining the antennas,and notional lines 110 joining the antennas to the obstacle, determinethe differences between the lengths (d1, d2 and d3) of the lines 110.Those differences are in effect measured by the radar system using thegating technique previously described.

The signal received from an obstacle depends on the transmitted power(Pt), the reflecting power of the obstacle (pobst), the gain of thetransmitting antenna (Gt (θ,φ)), the gain of the receiver (Gr (θ,φ)),the range from the receiver to the obstacle (Rro) and from thetransmitter to the obstacle (Rto), and the effective area of thereceiver (Ae), according to the equation:$\Pr = \frac{{Pt}*{{Gt}\left( {\theta,\varphi} \right)}*\left( {{{Gr}\left( {\theta,\varphi} \right)}*{Robst}*{Ae}} \right.}{4*\pi*{Rro}^{\hat{}}2*{Rto}^{\hat{}}2}$

Since the position of the obstacle, Pt, Ae and the gain of each antennaas a function of the polar angles θ (elevation) and φ (azimuth) areknown, the reflecting power can be calculated directly from the receivedpower, which is measured directly by the radar.

The invention thus provides a radar sensor which can be installed on amachine or vehicle to monitor different volumes of space near thevehicle, in which the special configuration of the radar permits it toperform a number of functions previously regarded as separate, dependingon the contents of the nearby space, and on the state of the vehicle.

What is claimed is:
 1. A radar system for installation on a vehicle orother mobile machine and for detecting objects in differing fields ofview of the system, the system comprising transceiver means fortransmitting a radar signal and receiving the signal after the latterhas been reflected from the reflecting surface of an object to bedetected; sampling means for sampling the output of the transceivermeans during a sampling period, which is delayed with respect to arespective portion of the transmitted signal by a time delaycorresponding to the time taken for that portion to travel to thereflecting surface when the latter is at a notional range shell, andthen back to the receiving means, so that a reflected signal receivedduring that period is indicative of the presence of a reflecting surfaceat the range shell, a respective field of view of the system beingconstituted by said range shell so that only reflecting surfaces on therange shell are detected; control means for controlling the position ofthe field of view of the system and sensor means which is connected tothe control means and is operable to detect at least one property of theoperation of the vehicle, wherein the control means in use determines arequired position of the field of view and sets the field of view of thesystem accordingly, in dependence on the output of the sensor means. 2.A system according to claim 1, in which the control means controls thefield of view by controlling said delay and hence the distance of therange shell from the system.
 3. A system according to claim 1, in whichthe transceiver means comprises at least one of a plurality oftransmitter antennas for transmitting said signals and a plurality ofreceiver antennas for receiving reflected signals, the control meansbeing operable to control the field of view by selecting which of thereceiver antennas is to be sampled by at least one of the sampling meansand which transmitter antenna is to transmit said signal.
 4. A radarsystem according to claim 3, in which, with the system installed on avehicle or object, the orientation of each antenna relative to thevehicle or object is fixed.
 5. A radar system according to claim 1, inwhich the radar system comprises an impulse radar system, in which thetransmitted signal comprises a succession of pulses, each of whichconstitutes a respective said portion of the transmitted signal.
 6. Aradar system according to claim 1, in which the control means, in use,detects fluctuations in the signal received in a succession of samplingperiods, said fluctuations corresponding to an object entering orleaving a range shell.
 7. A radar system according to claim 6, in whichthe control means, in use, also analyses the received signals todetermine at least one of the principal frequency thereof and the timedelay between detections at different range shells, and provides anestimate of the velocity of the object relative to the range shells. 8.A system according to claim 1, in which the control means in use,detects any DC offset of signal received over a succession of samplingperiods with respect to a reference level to determine whether there isan object at the range shell which object is stationary relative to therange shell.
 9. A radar system according to claim 1, in which the systemis for installation on a motor road vehicle.
 10. A radar systemaccording to claim 9, in which the transceiver means comprises aplurality of antennas for mounting on a vehicle in such a way that, inuse, the system is able to detect the presence of objects at anyposition around the vehicle, without altering the orientation of any ofthe antennas relative to the vehicle.
 11. A radar system according toclaim 10, in which the antennas are configured such that, when anantenna is mounted at a respective corner region of the vehicle, a 270°field of view is provided at that corner.
 12. A radar system accordingto claim 11, in which the antennas are incorporated into the vehiclebumpers.
 13. A radar system according to claim 10, in which thetransceiver means comprises two transmitter antennas adapted to bemounted at diagonally opposite corner regions of the vehicle, and tworeceiver antennas.
 14. A radar system according to claim 13, in whichthe sensor means includes sensors for detecting at least one of theoperation of the direction indicators and steering wheel movement of thevehicle, wherein the control means selects transmitter and receiverantennas to create range shells to the sides of the vehicle in responseto signals from said sensors.
 15. A radar system according to claim 9,in which the sensor means is operable to detect the selection of reversegear on the vehicle, and the control means selects a range shell behindthe vehicle in response to said selection.
 16. A radar system accordingto claim 9, in which the sensor means to detects the velocity of thevehicle, the control means selecting range shells at one or moredistances from the vehicle related to said velocity.
 17. A radar systemaccording to claim 9, in which the sensor means determines whether, andthe speed with which the vehicle is travelling.
 18. A system accordingto claim 17, in which the control means, in use, sets the range shell ata distance from the vehicle which increases with increasing speed of thevehicle in accordance with a predetermined relationship.
 19. A radarsystem according to claim 18, in which that relationship is one in whichthe range shell distance is directly proportional to said speed, subjectto a minimum range shell distance when the vehicle is stationary or slowmoving.
 20. A radar system according to claim 9, in which thetransceiver means comprises a plurality of receiver antennas formounting at different heights on the vehicle.
 21. A radar systemaccording to claim 20, in which said antennas are at least one oflaterally and vertically spaced from each other.
 22. A radar systemaccording to claim 21, in which the control means, in use, locates theposition of an obstacle sensed by the system relative to the vehicle andcalculates the reflective power of the obstacle using information onantenna sensitivities of the system at that position.
 23. A radar systemaccording to claim 1, in which the control means progressively increasesor decreases said time delay for successive periods so that thedistances of successive range shells progressively increase or decrease,so that the range shells scan a given area.
 24. A radar system accordingto claim 1, in which, upon detection of an obstacle at a given rangeshell, the control means is select further range shells in the vicinityof said given range shell so that the range shells, in effect, track theobstacle.
 25. A surface vehicle fitted with a radar detection systemaccording to claim 1, wherein the system comprises two transmitterantennas operable to transmit a series of pulses, and mounted atdiagonally opposed corner regions of the vehicle, and two receiverantennas, which are operable to receive pulses reflected from otherobjects and which are mounted at the other corner regions of thevehicle.
 26. A system according to claim 1, in which the system, in use,generates multiple range shells at different targets.